Several patents disclose panel displays using two-frequency upconversion fluorescence, such as U.S. Pat. Nos. 5,684,621; 5,764,403; 5,914,807; 5,943,160, and 5,956,172 all to Downing. Upconversion is generally the addition of two or more photons of light by a material. The upconversion material then emits one photon in response. A requirement for an upconversion material is that the emitted photon has a higher energy (shorter wavelength) than either of the excitation photons. For most applications, excitation photons are near infrared, with the emitted photons being in the visible range of the spectrum.
Although near infrared diodes are relatively simple and inexpensive, the light is not visible to an observer. Red, green and blue visible light laser sources are complex and expensive and produce light that an observer sees as speckled. Therefore, some display systems have been developed that employ the simplicity of the diode laser and yet yields full color, high resolution, high brightness, speckle free images.
For example, U.S. Pat. No. 6,327,074 B1 to Bass et al (Bass '704) is entitled “Display medium using emitting particles dispersed in a transparent host”. Bass '704 discloses two and three dimensional color image displays. The displays include a display medium comprising a plurality of pixels. Each pixel has a substantially uniform dispersion of red, green and blue visible light emitting particles therein sized between approximately 0.5 to approximately 50 microns. The particles disclosed include dye doped polymethylmethacrylate (pmma) plastic, and the display medium disclosed includes pmma, acrylic plastic or glass. Other particles can be used such as rare earth doped crystals. The two dimensional display disclosed uses three (3) remotely positioned laser sources each providing different emission wavelengths that are directed to each the respective pixels of the display medium using a scanning device. Light is absorbed by the particles which then become excited and emit visible fluorescence. The disclosed scanners and lenses move and focus the laser beams to different pixels in order to form the images having different visible colors.
Although Bass '704 is a significant advance in display technology, the plurality of separate system components, such as lasers, modulators, scanners and focus optics required results in a system size, complexity and cost which limits its use in certain applications. What is needed is a fully integrated upconversion material-based high resolution display. Such a display would provide mass production, small size and associated low cost, as well as being robust and highly reliability.